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Biomedical subjects

G Matsumoto

Publications and source records attributed to G Matsumoto.

At least 19 recordsLinked to original sources
PubMed1997

Molecular cloning and characterization of a putative neural calcium channel alpha1-subunit from squid optic lobe.

The complete amino acid sequence of a putative calcium channel alpha1-subunit, SQCC1, from the optic lobe of the squid Loligo bleekeri has been deduced by cloning and sequence analysis of the complementary DNA. The open reading frame encodes 2206 amino acids, which corresponds to a molecular weight of 251,451. The deduced amino acid sequence shares general structural features with the other voltage-dependent calcium channels; it consists of four repeated units of homology. Each motif has five hydrophobic segments and one positively charged segment. The transcriptional products were detected in all nervous systems examined; optic lobe, cerebral ganglia and giant stellate ganglia. However, it was not detected in the mantle muscle, heart and stomach, indicating SQCC1 is a calcium channel alpha1-subunit specific for squid nervous system. SQCC1 is more closely related in its amino acid sequence patterns to dihydropyridine-insensitive calcium channels rather than dihydropyridine-sensitive ones.

Amino Acid Sequence↗
PubMed1996

Enhanced fast synaptic transmission and a delayed depolarization induced by transient potassium current blockade in rat hippocampal slice as studied by optical recording.

In hippocampal neurons, a slowly inactivating aminopyridine-sensitive transient potassium current, D-current, influences the time course of action potential repolarization and therefore activity-dependent Ca2+ entry. We used high-speed optical recording techniques to study the effects of selectively inhibiting D-current with 4-AP (40 microM) on transmission at the Schaffer collateral (CA3)-CA1 synapse in rat hippocampal slices stained with the voltage-sensitive dye RH-155. We observed that addition of 4-AP to the bathing solution resulted in (1) augmentation of a fast component of the optical signal corresponding to the postsynaptic EPSP and action potential, and (2) the appearance of a delayed depolarization of CA1 neurons and other adjacent cells. 4-AP appeared to alter the presynaptic action potential and the dynamics of synaptic transmission to both reduce the sensitivity of the postsynaptic EPSP and action potential to omega-toxin calcium channel blockers (omega-conotoxin GVIA and omega-agatoxin IVA) and the Ca(2+)-dependent potassium channel blocker charybdotoxin, and to increase sensitivity to the dihydropyridine nifedipine, the NMDA receptor blocker aminophosphonopentanoic acid, and the intracellular Ca2+ release inhibitor thapsigargin. The delayed depolarization induced by 4-AP was inhibited in hyperosmotic extracellular solution, suggesting that enhanced transmitter release resulted in increased accumulation of K+ in the extracellular space. Because 4-AP is a convulsant at concentrations similar to those used here, we suggest that the 4-AP-targeted channel(s) carrying D-current may contribute to the hyperexcitability associated with epilepsy.

4-Aminopyridine↗
PubMed1996

Entorhinal-hippocampal interactions revealed by real-time imaging.

The entorhinal cortex provides the major cortical input to the hippocampus, and both structures have been implicated in memory processes. The dynamics of neuronal circuits in the entorhinal-hippocampal system were studied in slices by optical imaging with high spatial and temporal resolution. Reverberation of neural activity was detected in the entorhinal cortex and was more prominent when the inhibition due to gamma-aminobutyric acid was slightly suppressed. Neural activity was transferred in a frequency-dependent way from the entorhinal cortex to the hippocampus. The entorhinal neuronal circuit could contribute to memory processes by holding information and selectively gating the entry of information into the hippocampus.

Animals↗
PubMed1996

Increased c-fos expression in spinal neurons induced by electrical stimulation of the ureter in the rat.

The spinal processing of afferent input from the ureter was examined using an immunocytochemical technique to detect the expression of c-fos, an immediate early gene. Proximal and distal sites in one ureter were electrically stimulated separately or together at intensities that elicited a pseudo-affective response (an increase in arterial pressure). Very few Fos+ cells (range: 0.6-6.6 cells/half section were present in the L(1)-L(2), L(5)-S(2) spinal segments in sham operated control animals; however, following stimulation of the ureter, a significant increase in the numbers of Fos+ cells was detected at spinal levels L(1)-L(2) (mean 24.5-33.1 cells/half section) and L(6)-S(1) (mean 17.4-33.0 cells/half section). In L(6)-S(1), the numbers of Fos+ cells were significantly greater ipsilateral (mean 25.2 cells/half section) vs. contralateral (12.3 cells/half section) to stimulation; whereas in L(1)-L(2), the numbers were similar on both sides of the spinal cord. In L(1)-L(2), a greater percentage of Fos+ cells was present in superficial medial (MDH, 49.7%) and lateral dorsal horn (LDH, 40.8%); whereas in L(6)-S(1), the cells were more numerous in sacral parasympathetic nucleus (SPN, 38.7%) and LDH (25.6%*) regions. This distribution of Fos+ cells varies in a number of respects from that noted in previous experiments after chemical irritation of the urinary bladder and urethra which activated neurons only in L(6)-S(1) and primarily in the DCM and MDH. The results indicate that nociceptive afferent inputs from different areas of the urinary tract are processed in different regions of the spinal cord.

Animals↗
PubMed1996

Cultured giant fiber lobe of squid expresses three distinct potassium channel activities in selective combinations.

Neurons from the giant fiber lobe (GFL) of squid Loligo bleekeri were dissociated and cultured. The ionic currents were recorded using whole-cell patch clamp methods. The sodium current and the noninactivating potassium current like those elicited by the giant axon were among the currents expressed in axonal bulbs and bulblike structures upon dissociation. Meanwhile axonless cell bodies did not elicit such currents. Axonless cell bodies and some bulblike structures elicited two kinds of inactivating potassium currents, the slow- and the fast-inactivating current, which differed in their inactivation kinetics and pharmacology. Within 24 hr of plating, the current composition remained the same. While the noninactivating current was not sensitive to 4-aminopyridine, the two inactivating currents were sensitive, the slow-inactivating current being more sensitive. Selective combinations of the sodium current and the three potassium currents expressed in different structures of the acutely dissociated GFL could have resulted from cellular control of synthesis and transportation of the channel proteins to the somatic and the axonal membrane. The sodium current and the noninactivating potassium current could be recorded from some axonless cell bodies maintained in culture for over three days, indicating that the separation of the giant axon from its somata could result in the transportation of the channels normally expressed on the giant axon membrane to the somatic membrane.

4-Aminopyridine↗
PubMed1996

[Channel structure and functioning based on octagonal structure model].

On the basis of the sequence comparison of squid sodium channel SQSCl with those of other channels, we have proposed a tertiary structure model of the sodium channel where the transmembrane segments are octagonally aligned and the four linkers of S5-6 between segments S5 and S6 play a crucial role in the activation gate, voltage sensor and ion selective pore, which can slide, depending on membrane potentials, along inner walls consisting of segments S2 and S4 alternately. The proposed octagonal structure model is contrasted with that of Noda et al (Nature 320 : 188-192, 1986) and with Durrel and Guy (Biophys J 62 : 238-250, 1992). The octagonal structure model can explain the gating of activation and inactivation, the ion selectivity, and as well, the action mechanism of both tetrodotoxin (TTX) and a-scorpion toxin (ScTX), and be applied not only to the sodium channel, but also to the calcium channel, potassium channel, cGMP gated channel and further to the inwardly rectifying K channels. However Yan and Horn have discussed voltage dependent S4 movement in sodium channels from the accessibility of methanethiosulfonate (MTSET) to cystein residue which was substituted for the outermost arginine in IVS4 (Neuron 15 : 213-218, 1995), the neutralization of the arginine was revealed not to influence the activation of the channel. It suggest that the residue in the 3rd position of IVS4 is not a part of the voltage sensor located in the membrane. These result suggest that the change of the accessibility might be caused by the change of the covering of the residue rather than the movement of S4.

Amino Acid Sequence↗
PubMed1995

Non-NMDA glutamatergic excitatory transmission in the descending limb of the spinobulbospinal micturition reflex pathway of the rat.

I.v. administration of GYKI-52466, a non-competitive AMPA/kainate glutamatergic receptor antagonist, inhibited bladder contractions elicited by electrical stimulation in the pontine micturition center (PMC) in urethane-anesthetized rats. The mean threshold dose of GYKI-52466 was 2 mg/kg i.v. (range = 1-4 mg/kg). Maximum inhibition (mean = 57.7 +/- 8.2%, range = 24-83.3% of control) occurred at a dose of 8 mg/kg. CNQX, a competitive AMPA/kainate glutamatergic receptor antagonist, did not significantly alter the evoked contractions. These results indicate that AMPA/kainate receptors are involved in bulbospinal excitatory pathway from the PMC to the parasympathetic nucleus in the lumbosacral spinal cord in the rat.

Animals↗
PubMed1995

Neuronal specificity of subtype SQSC1 of squid putative sodium channel.

The distribution of SQSC1 mRNA in tissues of squid Loligo bleekeri was studied by the blot hybridization method. The complete cDNA for the coding region of SQSC1, the invertebrate putative sodium channel, was prepared from squid optic lobe (Sato and Matsumoto, Biochem. Biophys. Res. Comm. 186, 61-68, 1992). Transcriptional products of the SQSC1 gene were found to consist of two main different lengths (12 and 9 kb). The transcriptional products were detected in all the nervous tissues examined: optic lobes, cerebral ganglia and giant stellate ganglia. However, it was not detected in the muscle, suggesting the SQSC1 gene is specific for sodium channels of squid nerve cells. SQSC1 appears more widely distributed in the nervous system than GFLN1 which they reported as expressed specifically in stellate ganglion of the squid (Rosenthal and Gilly, Proc. Natl. Acad. Sci. USA 90, 10026-10030, 1993).

Alternative Splicing↗
PubMed1995

Role of glutamate and NMDA receptors in the descending limb of the spinobulbospinal micturition reflex pathway of the rat.

MK-801, an NMDA receptor antagonist administered intravenously or intrathecally to the L6-S1 spinal cord inhibited in a dose dependent manner the amplitude of isovolumetric bladder contractions evoked by electrical stimulation in the pontine micturition center (PMC) in urethane anesthetized rats. The mean threshold dose of MK-801 was 10 +/- 6 micrograms/kg i.v. and 10 +/- 1 micrograms i.t. Bladder contractions were completely inhibited at doses ranging from 300 to 3000 micrograms/kg i.v. and from 18 to 48 micrograms i.t. These data indicate that NMDA glutamatergic receptors play an important role in excitatory transmission in the descending pathway from the PMC to the spinal segmental circuitry involved in the control of the urinary bladder.

Animals↗
PubMed1995

Sodium channel functioning based on an octagonal structure model.

The complete amino acid sequence of a sodium channel from squid Loligo bleekeri has been deduced by cloning and sequence analysis of the complementary DNA. A unique feature of the squid sodium channel is the 1,522 residue sequence, approximately three-fourths of those of the rat sodium channels I, II and III. On the basis of the sequence, and in comparison with those of vertebrate sodium channels, we have proposed a tertiary structure model of the sodium channel where the transmembrane segments are octagonally aligned and the four linkers of S5-6 between segments S5 and S6 play a crucial role in the activation gate, voltage sensor and ion selective pore, which can slide, depending on membrane potentials, along inner walls consisting of alternating segments S2 and S4. The proposed octagonal structure model is contrasted with that of Noda et al. (Nature 320; 188-192, 1986). The octagonal structure model can explain the gating of activation and inactivation, and ion selectivity, as well as the action mechanism of both tetrodotoxin (TTX) and alpha-scorpion toxin (ScTX), and can be applied not only to the sodium channel, but also to the calcium channel, potassium channel and cGMP-gated channel.

Amino Acid Sequence↗
PubMed1994

Signal transmission in the parallel fiber-Purkinje cell system visualized by high-resolution imaging.

We investigated the synaptic transmission in the parallel fiber-Purkinje cell system at high spatio-temporal resolution by using voltage-sensitive dyes and an imaging system. In rat cerebellar slices, cut in the frontal plane or in a plane of the cerebellar surface, local electrical stimulation induced volleys of action potentials in the parallel fibers; subsequent postsynaptic responses from Purkinje cells were observed along the volleys' entire trajectories. Furthermore, the formation of an ordered spatial gradient in parallel fiber conduction velocity across the depth of the molecular layer during postnatal development was observed. In preparations of adult, but not of immature rats, the conduction velocity of parallel fibers in the deep molecular layer was faster than in its more superficial regions. Our observations demonstrate that parallel fibers can mediate Purkinje cell excitation effectively and over considerable distances in a well-organized spatio-temporal manner, thus supporting the classical view of the physiological role assigned to the parallel fibers.

Action Potentials↗
PubMed1994

Nicardipine may impair glucose metabolism in hypertensive diabetic patients.

The respective effects of 6 month's administration of beta-blockers (atenolol, metoprolol, carteolol and arotinolol), calcium-channel blockers (nicardipine, diltiazem) and angiotensin converting enzyme inhibitor (enalapril) on hemoglobin A1c (HbA1c) levels were evaluated in hypertensive patients with non-insulin-dependent diabetes mellitus (NIDDM), using a retrospective method. NIDDM patients with stable HbA1c and body weight were selected for this study. The following results were obtained. (1) The administration of nicardipine or beta-blockers significantly elevated HbA1c levels. (2) The administration of diltiazem or enalapril did not have any influence on HbA1c levels. These findings suggest that not only beta-blocker but nicardipine (dihydropyridine type calcium-channel blocker) may cause deterioration in glucose metabolism in NIDDM patients.

Adult↗
PubMed1992

Proposed tertiary structure of the sodium channel.

On the basis of our recent results of the complete amino acid sequence of the squid Loligo bleekeri sodium channel deduced by cloning and sequence analysis of the complementary DNA (Sato, C. and Matsumoto, G. Biochem. Biophys. Res. Comm. 186, 1), we have proposed a tertiary structure model of the sodium channel where the transmembrane segments are octagonally aligned and the four linkers of S5-6 between segments S5 and S6 play a crucial role in the activation gate, voltage sensor and ion selective pore, which can slide, depending on membrane potentials, along inner walls consisting of segments S2 and S4 alternately. The proposed model is contrasted with that of Noda et al. (Nature 320; 188-192, 1986).

Amino Acid Sequence↗
PubMed1992

Primary structure of squid sodium channel deduced from the complementary DNA sequence.

The complete amino acid sequence of a sodium channel from squid Loligo bleekeri has been deduced by cloning and sequence analysis of the complementary DNA. The deduced sequence revealed an organization virtually identical to the vertebrate sodium channel proteins; four homologous domains containing all six membrane-spanning structures are repeated in tandem with connecting linkers of various sizes. A unique feature of the squid Na channel is the 1,522 residue sequence, approximately three fourths of those of the rat sodium channels I, II and III.

Amino Acid Sequence↗
PubMed1992

Synaptic activation of rat adrenal medulla examined with a large photodiode array in combination with a voltage-sensitive dye.

The adrenal medulla is innervated by sympathetic preganglionic nerve fibers in the splanchnic nerve. Synaptic activation of the adrenal medulla causes catecholamine secretion which is known to be modified by various neuropeptides and other factors. To understand the neuronal control mechanism of catecholamine secretion, it is necessary to know the transfer function at the synapse and how it is affected by such factors. By using a large photodiode array in combination with a voltage-sensitive dye, membrane potential changes in a slice of the rat adrenal gland were recorded upon brief local electrical stimulation. Electrical signals were recorded only on the portion of the diode array corresponding to the medulla. In a typical record, a spike and an underlying slow potential were observed following a small deflection due to a presynaptic nerve action potential. Both the spike and slow potential were blocked in Ca(2+)-free solution or by hexamethonium, a nicotinic antagonist, but were not affected by atropine, a muscarinic antagonist. The slow potential was interpreted as a nicotinic synaptic potential in the chromaffin cells and the spike as a population action potential. A double pulse experiment revealed that the chromaffin cell action potential began to fail only when the stimulus interval was less than 50 ms (20 Hz). When the stimulus intensity was reduced, the minimal response was found to behave in an all-or-none fashion. This suggested that one nerve fiber is innervating a cluster of chromaffin cells, which may correspond to a previously histologically identified "complex" of cells [Hillarp (1946) Acta. anat. 4, Suppl. 1]. Each complex was innervated by approximately four nerve fibers.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenal Medulla↗